使用 lxml 解析 html答案

【问题标题】：parsing html using lxml使用 lxml 解析 html
【发布时间】：2012-09-23 12:08:36
【问题描述】：

我有以下html代码

<a name="Audio-Encoders"></a>
<h1 class="chapter"><a href="ffmpeg.html#toc-Audio-Encoders">14. Audio Encoders</a></h1>

<p>A description of some of the currently available audio encoders
follows.
</p>
<a name="ac3-and-ac3_005ffixed"></a>
<h2 class="section"><a href="ffmpeg.html#toc-ac3-and-ac3_005ffixed">14.1 ac3 and     ac3_fixed</a></h2>

<p>AC-3 audio encoders.
</p>
<p>These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as well as
the undocumented RealAudio 3 (a.k.a. dnet).
</p>
<p>The <var>ac3</var> encoder uses floating-point math, while the <var>ac3_fixed</var>
encoder only uses fixed-point integer math. This does not mean that one is
always faster, just that one or the other may be better suited to a
particular system. The floating-point encoder will generally produce better
quality audio for a given bitrate. The <var>ac3_fixed</var> encoder is not the
default codec for any of the output formats, so it must be specified explicitly
using the option <code>-acodec ac3_fixed</code> in order to use it.
</p>
<a name="AC_002d3-Metadata"></a>
<h3 class="subsection"><a href="ffmpeg.html#toc-AC_002d3-Metadata">14.1.1 AC-3     Metadata</a></h3>

<p>The AC-3 metadata options are used to set parameters that describe the audio,
but in most cases do not affect the audio encoding itself. Some of the options
do directly affect or influence the decoding and playback of the resulting
bitstream, while others are just for informational purposes. A few of the
options will add bits to the output stream that could otherwise be used for
audio data, and will thus affect the quality of the output. Those will be
indicated accordingly with a note in the option list below.
</p>
<p>These parameters are described in detail in several publicly-available
documents.
</p><ul>

如何从<hX class="foobar">之后的每一个之后提取文本？

例如<h1 class="chapter"> h1标签后的内容是“一些当前可用的音频编码器的描述跟随。”

【问题讨论】：

那是无效的 HTML。
我把问题改了更清楚，谢谢回复
这再清楚不过了；请让您的问题自成一体，而不是依赖于其他网站（这可能会或可能不会随着时间的推移而改变，从而使您的问题无效）。
我再次将问题更改为一个独立的问题
ffmpeg 文档以 TextInfo 格式 (git.videolan.org/?p=ffmpeg.git;a=tree;f=doc) 提供，这比生成的 HTML 更容易解析。

标签： python xpath lxml

【解决方案1】：

使用：

/*/h1/following-sibling::p
         [name(preceding-sibling::*[starts-with(name(),'h')][1])
         = 'h1'
         ]//text()

根据以下 XML 文档评估此 XPath 表达式（从提供的格式不正确的片段中获得，即删除尾随未闭合的 ul 并将结果包装到单个顶部元素中）：

<html>
    <a name="Audio-Encoders"></a>
    <h1 class="chapter">
        <a href="ffmpeg.html#toc-Audio-Encoders">14. Audio Encoders</a>
    </h1>
    <p>A description of some of the currently available audio encoders follows. </p>
    <a name="ac3-and-ac3_005ffixed"></a>
    <h2 class="section">
        <a href="ffmpeg.html#toc-ac3-and-ac3_005ffixed">14.1 ac3 and     ac3_fixed</a>
    </h2>
    <p>AC-3 audio encoders. </p>
    <p>These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as well as the undocumented RealAudio 3 (a.k.a. dnet). </p>
    <p>The 
        <var>ac3</var> encoder uses floating-point math, while the 
        <var>ac3_fixed</var> encoder only uses fixed-point integer math. This does not mean that one is always faster, just that one or the other may be better suited to a particular system. The floating-point encoder will generally produce better quality audio for a given bitrate. The 
        <var>ac3_fixed</var> encoder is not the default codec for any of the output formats, so it must be specified explicitly using the option 
        <code>-acodec ac3_fixed</code> in order to use it. 
    </p>
    <a name="AC_002d3-Metadata"></a>
    <h3 class="subsection">
        <a href="ffmpeg.html#toc-AC_002d3-Metadata">14.1.1 AC-3     Metadata</a>
    </h3>
    <p>The AC-3 metadata options are used to set parameters that describe the audio, but in most cases do not affect the audio encoding itself. Some of the options do directly affect or influence the decoding and playback of the resulting bitstream, while others are just for informational purposes. A few of the options will add bits to the output stream that could otherwise be used for audio data, and will thus affect the quality of the output. Those will be indicated accordingly with a note in the option list below. </p>
    <p>These parameters are described in detail in several publicly-available documents. </p>
</html>

选择想要的文本节点（在这种情况下只有一个）：

A description of some of the currently available audio encoders follows.

同样，这个 XPath 表达式：

/*/h2/following-sibling::p
         [name(preceding-sibling::*[starts-with(name(),'h')][1])
         = 'h2'
         ]//text()

选择这些文本节点：

AC-3 audio encoders. These encoders implement part of ATSC A/52:2010 and ETSI TS 102 366, as well as the undocumented RealAudio 3 (a.k.a. dnet). The 
        ac3 encoder uses floating-point math, while the 
        ac3_fixed encoder only uses fixed-point integer math. This does not mean that one is always faster, just that one or the other may be better suited to a particular system. The floating-point encoder will generally produce better quality audio for a given bitrate. The 
        ac3_fixed encoder is not the default codec for any of the output formats, so it must be specified explicitly using the option 
        -acodec ac3_fixed in order to use it.

最后，这个 XPath 表达式：

/*/h3/following-sibling::p
         [name(preceding-sibling::*[starts-with(name(),'h')][1])
         = 'h3'
         ]//text()

选择这些文本节点：

The AC-3 metadata options are used to set parameters that describe the audio, but in most cases do not affect the audio encoding itself. Some of the options do directly affect or influence the decoding and playback of the resulting bitstream, while others are just for informational purposes. A few of the options will add bits to the output stream that could otherwise be used for audio data, and will thus affect the quality of the output. Those will be indicated accordingly with a note in the option list below. These parameters are described in detail in several publicly-available documents.

【讨论】：

感谢您的精彩回答，但我正在尝试使用 xpath 做类似 bpaste.net/show/v1xL6rDXJ16LedIm3Gm5 的事情
@PerguntasEasy，然后只需删除每个表达式末尾的字符串//text()。